As an electric motor of a type that generates a rotational force by utilizing a difference in magnetic resistance between a stator and a rotor, a reluctance motor has been known. In the reluctance motor, reluctance torque generated by the difference in magnetic resistance is used to rotate the rotor. However, since the reluctance torque is smaller than torque obtained by a magnet, compared with a motor of the same physical structure which uses a magnet, the output torque of the reluctance motor tends to be smaller. Therefore, the problem is that, in order to achieve a desired torque with the reluctance motor, the structure of the motor becomes larger.
In recent years, a magnet-assisted reluctance motor has been proposed, with a magnet being disposed on a rotor in the basic configuration of a reluctance motor. For example, Patent Document 1 discloses such a magnet-assisted reluctance motor, and shows a magnet embedded in a rotor of the reluctance motor. In the case of the motor of Patent Document 1, in one of the magnetic poles, i.e. N- or S-pole, of a rotor core, a first permanent magnet, which is high in magnetic flux density and is made of the same magnet material and has the same shape, is embedded. In the other magnetic pole, a second permanent magnet, which is different in shape from the first permanent magnet, is embedded. The second permanent magnet is made of the same magnet material that is low in magnetic flux density. According to this configuration, the reluctance motor uses assistance of the magnetic force from the magnet, and rotates the rotor with both the reluctance torque and the magnet torque, thereby leading to both an improvement in the output and a reduction in the size of the motor.